Optic spacing nubs

ABSTRACT

A solar energy system, including a front panel and at least two mirrors, is provided. The mirrors are used to focus light onto a photoconductive cell. In the preferred embodiment, three or more nubs are an integral part of at least one of the mirrors. When the system is assembled, these nubs are configured between the panel and a mirror to provide a substantially uniform gap for an adhesive. The mirror is secured to the panel by the adhesive. Thus, the nubs assist with desired attachment and alignment of a mirror to the panel in the solar energy system.

BACKGROUND OF THE INVENTION

It is generally appreciated that one of the many known technologies forgenerating electrical power involves the harvesting of solar radiationand its conversion into direct current (DC) electricity. Solar powergeneration has already proven to be a very effective and“environmentally friendly” energy option, and further advances relatedto this technology continue to increase the appeal of such powergeneration systems. In addition to achieving a design that is efficientin both performance and size, it is also desirable to provide powerunits and corresponding solar systems that are characterized by reducedcost and increased levels of mechanical robustness.

Solar concentrators are solar energy generators which increase theefficiency of conversion of solar energy to DC electricity. Solarconcentrators which are known in the art utilize parabolic mirrors andFresnel lenses for focusing the incoming solar energy, and heliostatsfor tracking the sun's movements in order to maximize light exposure. Anew type of solar concentrator, disclosed in U.S. patent applicationSer. No. 11/138,666, entitled, “Concentrator Solar Photovoltaic Arraywith Compact Tailored Imaging Power Units” utilizes a front panel forallowing solar energy to enter the assembly, with a primary mirror and asecondary mirror to reflect and focus solar energy onto a solar cell. Aback panel and housing enclose the assembly and provide structuralintegrity. The surface area of the solar cell in such a system is muchsmaller than what is required for non-concentrating systems, for exampleless than 1% of the entry window surface area. Such a system has a highefficiency in converting solar energy to electricity due to the focusedintensity of sunlight, and also reduces cost due to the decreased amountof costly photovoltaic cells required. Because the receiving area of thesolar cell is so small relative to that of the power unit, the abilityof the mirrors to accurately focus the sun's rays onto the solar cell isimportant to achieving the desired efficiency of such a solarconcentrating system.

In this type of solar concentrator panel, one of the key factors inmirror alignment is the process by which a mirror is adhered to thefront or back panel. Uncontrolled adhesive application may result invariations in adhesive thickness across the bonding area of the mirror,which in turn may affect the alignment of the mirror as well as the bondstrength which is important for withstanding high temperature conditionsin the solar power assembly. In another instance, the proper amount ofadhesive may be applied, but pressing the mirror and panel together inan uncontrolled manner may cause the adhesive to be exuded beyond thedesired bond area and into the clear aperture of the system. Difficultyin attaining consistent adhesive application can decreasemanufacturability and thus the commercial feasibility of such a design.

One solution to this problem of mirror alignment and attachment is usingspacers to set the distance between the mirror and panel to which it isto be bonded. U.S. Pat. No. 5,433,911 entitled “Precisely Aligning andBonding a Glass Cover Plate Over an Image Sensor” discloses anelectronics package which includes a spacer plate, a glass cover plate,an image sensor, and a carrier. In order to achieve the tight tolerancesfor spacing and parallelism which are required to align the variousplanar components in this assembly, precision ground and lapped spacersare used. While the spacers result in the desired alignment and spacingbetween the plates and image sensor, the precision to which they must bemade and the accuracy with which they are mounted increase the labor andcost of the assembly. The fact that the spacers are separate componentsalso adds complexity to the manufacturing process.

Spacer particles are another approach to setting uniform distancesbetween surfaces. U.S. Pat. No. 7,102,602 entitled “Doubly CurvedOptical Device for Eyewear and Method for Making the Same” discloses apair of substrates sealed together by a fluid material with spacersdisbursed therein. The substrates thus have a uniform controlleddistance there between due to the presence of the spacers. The spacersmay be placed between the substrates prior to application of the fluid,or they may be mixed into the fluid material first and then applied tothe unopposed substrates. While spacer particles are useful in settingthe gap of a critical dimension, an assembly with more than one criticaldimension would require specifically-sized spacer particles for eachapplication. Such a situation raises the likelihood for potentialmanufacturing errors should one spacer size be mistakenly used in placeof another size. Furthermore, each batch of adhesive would requireverification of the proper ball diameter, and the step of mixing spacersinto the fluid or adhesive adds labor to the manufacturing process.

Thus it is desirable to facilitate reliable alignment and attachment ofthe mirrors in a solar energy system in a manner which enhancesmanufacturability and therefore reduces overall cost and improvesmechanical robustness.

SUMMARY OF THE INVENTION

The present invention is a solar energy system, including a front paneland at least one mirror. In the preferred embodiment, three or more nubsare an integral part of the mounting surface of the mirror. When thesystem is assembled, these nubs are configured between the panel and themirror and provide a substantially uniform gap for an adhesive. Themirror is secured to the panel by the adhesive. Thus, the nubs assistwith desired attachment and alignment of the mirror to the panel in thesolar energy system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a perspective illustration of an exemplary embodiment ofthe solar power unit;

FIG. 2 shows a cross-sectional view of the assembly of FIG. 1, withadditional housing components;

FIG. 3 illustrates a side view of a secondary mirror with nubs mountedonto a front panel;

FIG. 4 provides a plan view of one embodiment of nubs on a secondarymirror;

FIG. 5A gives a perspective view of an alternative embodiment of asecondary mirror;

FIG. 5B is a cross-sectional view of the embodiment of FIG. 5A;

FIG. 6 shows a perspective view of an exemplary primary mirror with nubson its perimeter;

FIG. 7 shows an exploded perspective view of an embodiment of theassembly process for aligning and attaching a secondary mirror onto afront panel; and

FIG. 8 is a simplified flowchart illustrating basic steps in thefabrication process.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference now will be made in detail to embodiments of the disclosedinvention, one or more examples of which are illustrated in theaccompanying drawings. Each example is provided by way of explanation ofthe present technology, not limitation of the present technology. Infact, it will be apparent to those skilled in the art that modificationsand variations can be made in the present technology without departingfrom the spirit and scope thereof. For instance, features illustrated ordescribed as part of one embodiment may be used on another embodiment toyield a still further embodiment. Thus, it is intended that the presentsubject matter covers such modifications and variations as come withinthe scope of the appended claims and their equivalents.

The alignment and attachment means described in this disclosure arebased on a solar power unit design incorporating optically alignedprimary and secondary mirrors. The solar power unit design is describedin detail in related, co-pending patent applications as follows: (1)“Concentrator Solar Photovoltaic Array with Compact Tailored ImagingPower Units;” Ser. No. 11/138,666; filed May 26, 2005; and (2) “OpticalSystem Using Tailored Imaging Designs;” Ser. No. 11/351,314; filed Feb.9, 2006, which claims priority from U.S. provisional patent application60/651,856 filed Feb. 10, 2005; all of which are hereby incorporated byreference as set forth in full in this application for all purposes.

Note that variations on the design described in the priorityapplications may be achieved by modifing specific steps and/or itemsdescribed herein while still remaining within the scope of the inventionas claimed.

With reference to FIG. 1, a simplified perspective view of an exemplarysolar power unit 100 is shown. The main optical elements of the powerunit 100 are a protective front panel 110, a primary mirror 120, asecondary mirror 130, and a receiver assembly 140. Note that forcommercial application, the single power unit 100 would typically bereplicated to form an array of adjoining power units as part of acomplete solar panel. Protective front panel 110 is a substantiallyplanar surface, such as a window or other transparent covering, whichprovides structural integrity for a power unit and protection for othercomponents thereof In a preferred embodiment, front panel 110 iscomposed of glass; however, any type of transparent or transmissiveplanar sheet, such as polycarbonate, may be suitable for use in thesolar power unit. Sunlight enters the solar unit 100 through front panel110 and reflects off of primary mirror 120 to secondary mirror 130,where it is further reflected and focused onto receiver assembly 140. Inthe preferred embodiment, receiver assembly 140 houses an optical rodand a photovoltaic cell where the intensified sunlight is converted intoelectrical energy.

In reference still to FIG. 1, primary mirror 120 and secondary mirror130 are substantially co-planar, at least a portion of both mirrorsbeing in contact with front panel 110. In the depicted configuration,primary mirror 120 is generally circular such that the entire perimeter160 of primary mirror 120 is contact with front panel 110. Primarymirror 120 is preferably a second surface mirror using, for example,silver, and slump-formed from soda-lime glass. In one exemplaryembodiment, primary mirror 120 may have a diameter of approximately 280mm and a depth of approximately 70 mm. Secondary mirror 130 is alsogenerally circular, and is typically a first surface mirror using silverand a passivation layer formed on a substrate of soda-lime glass. In apreferred embodiment, secondary mirror 130 may have a diameter ofapproximately 50 mm. Nubs 150, to be described in further detail inreference to later figures, are present on the surface of secondarymirror 130 which is facing panel 110.

Turning now to FIG. 2, a cross-sectional view of a solar power unit 200is shown. The same elements given in FIG. 1 of a front panel 210,primary mirror 220, secondary mirror 230 with nubs 250, and receiverassembly 240 are shown. In the view provided in FIG. 2, however, theadditional components of a housing 260 and back panel 270 areillustrated in basic form. Housing 260 may be built from more than onepiece of material, such as but not limited to stamped metal orpolyethylene terephthalate (PET) and is designed to accommodate thetotal number of power units provided in a given solar energy system. Thehousing contains a lip 262 that allows the front panel 210 to bemounted, preferably with a rubber gasket (not shown) to seal the edgesof panel 210. Back panel 270, which may also be referred to as a baseplate, serves as a heat dissipation element for the solar unit and maybe formed of phosphor-bronze or an aluminum alloy. Housing 260 and backpanel 270 may be secured to the solar energy system by bolts, screws, orsimilar means (not shown) well-known in the art.

FIG. 3 provides a closer view of secondary mirror 330 and front panel310. Nubs 350 are shown as projections from mounting surface 340 ofsecondary mirror 330. Nubs 350 can be separate pieces from the secondarymirror 330, or are preferably integrally fabricated as part of secondarymirror 330. By having nubs 350 integral to secondary mirror 330, anymanufacturing tolerances resulting from either fabricating separate nubcomponents or adhering nubs 350 to surface 340 are eliminated. Integralnubs fabrication could entail the nubs 350 being molded into the shapeof the mirror 330 during the mirror pressing process. Alternatively,nubs 350 could be separate components that are insert-molded into themirror during the pressing process. The height of nubs 350 aresubstantially equal, which advantageously sets a substantially uniformgap between mounting surface 340 of secondary mirror 330, and bottomsurface 360 of front panel 310. This uniform gap thereby substantiallyaligns secondary mirror 330 in parallel to front panel 310. In a typicalembodiment, the distance between mounting surface 340 of secondarymirror 330 and back surface 360 of the front panel 310 is 50 microns to2.0 mm. Secondary mirror is secured to front panel 310 by adhesive 320,which fills the space between surfaces 340 and 360. In a preferredembodiment, silicone adhesive is used; however, any adhesive (epoxies,RTV, acrylics, etc.) which is appropriate for the substrates andoperating conditions of this assembly may be utilized.

FIG. 4 next illustrates a plan view of the mounting surface of secondarymirror 410. In this embodiment, three nubs 420 are shown to be equallydistributed near the circumference 430 of the mirror 410. The presenceof three nubs 420 establishes the planar stability of secondary mirror410. Alternatively, more than three nubs may be used for aiding thevisual inspection that nubs 420 are contacting the front panel (surface360 of FIG. 3), or for mechanical redundancy should any of the nubs 410be damaged during the manufacturing process. While the placement of nubs410 near circumference 430 as shown is desirable for increasing planarstability, the nubs may be placed in other configurations away from thecircumference. For example, a nub positioned in the center of thesecondary mirror 410 could be used to help center the secondary mirroronto the front panel. In another instance, the placement of nubs canassist in outlining the zones in which adhesive is to be dispensed.

Still referring to FIG. 4, nubs 420 are shown to be circular. However,other shapes may be used, such as rectilinear footprints, or even ahemispherical nub wherein the contact surface with the front panel wouldbe a point. The specific cross-sectional area of nubs 420 chosen wouldbe determined by the level of visual inspection desired as well as bythe manufacturing limitations of the process by which the secondarymirror is fabricated. Also to be taken into account is that the shapeand size of the nubs should not be conducive to damaging the panel,which may be glass, against which they are being placed. Furthermore,the impact of the total surface area occupied by the nubs would need tobe considered so as not to impact the bond strength of this joint.

FIG. 5A depicts an alternative embodiment of the secondary mirror 510.While previous embodiments have shown secondary mirror 510 to be a solidentity, FIG. 5 shows secondary mirror 510 in the case where it ishollow. Moreover, an alternative nubs embodiment consisting of four nubsbeing present and equally distributed around the mounting surface 530 ofsecondary mirror 510 is given. In this exemplary embodiment depicted incross-section in FIG. 5B, nubs 520 are integral to secondary mirror 510.That is, nubs 520 are formed during the fabrication of secondary mirror510. The nubs 520 are shown to be cylindrical in nature, but aspreviously described, they may take the form of rectilinear or othershapes as desired to facilitate fabrication of the secondary mirror, orto aid in the process of assembling the solar power unit. Edges 540 ofnubs 520, in this embodiment as well as others described in thisdisclosure, are preferably filleted to prevent damage to the front panelwhen the mirror 510 is placed in contact with the front panel.

FIG. 6 illustrates a further embodiment of primary mirror 610. In thisembodiment, primary mirror 610 is shaped such that there are truncatedsections 620 of the curved primary mirror 610. The truncated sectionsadvantageously allow adjacent power units to fit tightly together in asolar array, thus maximizing the number of power units which can bepacked into a solar energy system. For example, in the depictedconfiguration where there are four truncated sections, adjacent powerunits would fit together to form an orthogonal grid. The peaks of thetruncated sections terminate in flat mounting tabs 630, upon which nubs640 are placed or formed. In the truncated design, only the mountingtabs 630 with the nubs 640, rather than the entire perimeter of primarymirror 610, are in contact with the front panel. The heights of nubs 640are substantially equal, thus setting a substantially uniform gap foradhesive to be applied, and thus substantially aligning the primarymirror to the front panel.

Returning to the secondary mirror, FIG. 7 gives an exploded view of atemplate tool being used in the manufacturing process to securesecondary mirror 710 to front panel 720. Template tool 730 includes aprecision cutout 740 for centering secondary mirror 710 over thetransparent front panel 720. It should be appreciated that formanufacturing an array of solar power units, the template tool 730 wouldincorporate multiple cutouts 740 for the multiple mirrors in the array.Template tool 730 could also be a part of a larger tool which includesadditional functionality. While cutout 740 provides for proper planarpositioning along the face of front panel 720, nubs 750 ensure that themounting surface 760 of secondary mirror 710 is aligned substantiallyparallel to front panel 720. That is, nubs provide alignment in the axisperpendicular to the front panel. Placement of the mirror 710 onto thefront panel 720 could be achieved by automated machinery, in which casethe fixed spacing provided by the nubs would have further importance inmanufacturing reliability.

FIG. 8 is a simplified flowchart illustrating the basic steps insecuring a mirror to the front panel. In FIG. 8, flowchart 800 isentered at step 810. Step 820 is first performed to position thetemplate tool over the front panel. This can be accomplished byregistering the template tool with the front panel using visual,mechanical, or other means well-known in the art (pin registration,magnetic or other sensing, etc.). Next, if the nubs are not integral tothe mirror, step 830 is performed to fix the nubs onto the mirror. Instep 840, adhesive is dispensed onto either the front panel or mirror.Typically, the adhesive is dispensed in a discrete location or locationssuch as lines or dots. In step 850, the mirror is placed on the frontpanel through the aforementioned cutout on the template tool. Step 860is then performed to distribute the adhesive over the mounting surfaceof the secondary mirror. For example, in the case of a solid secondarymirror (FIG. 4), the adhesive could be first applied in two linesforming an “X” in step 840. Then, rotating the mirror in step 860 woulddistribute the adhesive across the circular mounting surface. In thecase of a hollow secondary mirror (FIG. 5A), the adhesive could bedispensed in dots between the nubs. Rotation of the mirror in step 860would then distribute the adhesive around the perimeter of the mirror'smounting surface. In an alternative embodiment, after the adhesive isapplied, compression may be used to distribute the adhesive between themounting surface of the mirror and the front panel. This pressure couldbe applied through the mirror, through the front panel or from bothsides.

Still referring to FIG. 8, step 870 provides verification of properadhesion. In the preferred embodiment, after the adhesive has beendistributed the operator would verify in step 870 whether the nubs arein full contact with the front panel. Verification methods could includea qualitative visual check, or quantitative means such as measurement ofthe mirror height before and after bonding. Failure for all nubs to bein contact would imply that a uniform adhesive gap has not beenachieved, and that the mirror is misaligned. In this case, step 880calls for adjusting mirror placement. Adjustment could involve suchmeasures as applying more pressure to the mirror or removing excessadhesive which may have seeped under the nubs. Once it is verified thatnubs are properly in contact with the front panel, the subassembly iscomplete.

Although embodiments of the invention have been discussed primarily withrespect to specific embodiments thereof, other variations are possible.Lenses or other optical devices might be used in place of, or inaddition to, the primary and secondary mirrors or other componentspresented herein. For example, a Fresnel type of lens could be used tofocus light on the primary optical element, or to focus light at anintermediary phase after processing by a primary optical element. Beyondsolar energy systems, nubs may be used to align a lens in an opticalassembly, or to provide spacing with respect to mating components.

It may be possible to use non-planar materials and surfaces with thetechniques disclosed herein. Other embodiments can use optical or othercomponents for focusing any type of electromagnetic energy such asinfrared, ultraviolet, radio-frequency, etc. There may be otherapplications for the fabrication method and apparatus disclosed herein,such as in the fields of light emission or sourcing technology (e.g.,fluorescent lighting using a trough design, incandescent, halogen,spotlight, etc.) where the light source is put in the position of thephotovoltaic cell. In general, any type of suitable cell, such as aphotovoltaic cell, concentrator cell or solar cell can be used. In otherapplications it may be possible to use other energy such as any sourceof photons, electrons or other dispersed energy that can beconcentrated.

Steps may be performed by hardware or software, as desired. Note thatsteps can be added to, taken from or modified from the steps in thisspecification without deviating from the scope of the invention. Ingeneral, any flowcharts presented are only intended to indicate onepossible sequence of basic operations to achieve a function, and manyvariations are possible.

While the specification has been described in detail with respect tospecific embodiments of the invention, it will be appreciated that thoseskilled in the art, upon attaining an understanding of the foregoing,may readily conceive of alterations to, variations of, and equivalentsto these embodiments. These and other modifications and variations tothe present invention may be practiced by those of ordinary skill in theart, without departing from the spirit and scope of the presentinvention, which is more particularly set forth in the appended claims.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

1. A solar power unit, comprising: a substantially planar surface; aprimary mirror radially symmetric about a first axis, said primarymirror having a perimeter wherein at least a portion of said perimeteris attached to said planar surface; a secondary mirror radiallysymmetric about a second axis, said secondary mirror having a mountingsurface wherein at least a portion of said mounting surface is attachedto said planar surface; three nubs on said mounting surface, said nubshaving nub heights, wherein said nub heights are substantially equal;and an adhesive substance; wherein said secondary mirror is secured tosaid planar surface by said adhesive substance, and wherein said nubsprovide a substantially uniform gap between said mounting surface andsaid planar surface for said adhesive substance.
 2. The solar power unitof claim 1, wherein said nubs are integral to said secondary mirror. 3.The solar power unit of claim 1, wherein said primary mirror and saidsecondary mirror focus light on a photovoltaic cell.
 4. The solar powerunit of claim 1, wherein said nub heights determines the bond thicknessof said adhesive.
 5. The solar power unit of claim 1, wherein said firstaxis is coaxial to said second axis.
 6. A method of attaching andaligning a mirror with integral nubs to a panel of a solar power unit,comprising: dispensing an adhesive onto said panel; positioning saidmirror over said panel; placing said mirror with said integral nubs incontact with said adhesive; distributing said adhesive; and confirmingcontact of said nubs with said panel; wherein said integral nubs havenub heights, and wherein said nub heights provide a substantiallyuniform gap in which to distribute said adhesive substance.
 7. Themethod of claim 6, wherein said mirror is a curved primary mirror with aperimeter, wherein said nubs are configured on said perimeter of saidprimary mirror, and wherein said nub heights are substantially equal. 8.The method of claim 7, wherein four nubs are configured on saidperimeter of said curved primary mirror.
 9. The method of claim 6,wherein said mirror is a curved secondary mirror with a mountingsurface, wherein said nubs are configured on said mounting surface ofsaid secondary mirror, and wherein said nub heights are substantiallyequal.
 10. The method of claim 9, wherein three nubs are configured onsaid mounting surface of said curved secondary mirror.
 11. The method ofclaim 6, wherein said distributing of said adhesive comprises rotatingsaid mirror.
 12. The method of claim 6, wherein said distributing ofsaid adhesive comprises compression.
 13. A solar energy system,comprising: a panel; a mirror having a mounting surface; three nubs withnub heights, wherein said nubs are integral to said mounting surface ofsaid mirror; and an adhesive substance, wherein said mirror is securedto said panel by said adhesive substance, and wherein said nub heightsprovide a substantially uniform gap between said panel and said mountingsurface of said mirror.
 14. The solar energy system of claim 13, whereinsaid nub heights determine the bond thickness of said adhesivesubstance.
 15. The solar energy system of claim 13, wherein said mirroris a curved primary mirror with a perimeter, wherein said nubs heightsare substantially equal, and wherein said nubs are configured on saidperimeter of said primary mirror.
 16. The solar energy system of claim13, wherein said mirror is a curved secondary mirror with a mountingsurface, wherein said nub heights are substantially equal, and whereinsaid nubs are configured on said mounting surface of said secondarymirror.
 17. The solar energy system of claim 13, wherein said mirrordirects light to a photovoltaic cell.
 18. The solar energy system ofclaim 13, wherein said mirror is symmetric about a first axis; andfurther comprising a secondary mirror symmetric about a second axissubstantially coaxial to said first axis, said secondary mirror having amounting surface wherein at least a portion of said mounting surface isattached to said panel.
 19. A solar energy system comprising; a panel; apressed optic having a mounting surface; multiple nubs with nub heights,wherein said nubs are integrally formed on said mounting surface; anadhesive substance, wherein said pressed optic is secured to said panelby said adhesive substance, and wherein said nub heights establish aspacing between said mounting surface and said panel.
 20. The solarenergy system of claim 19, wherein said pressed optic is a mirror. 21.The solar energy system of claim 19, wherein said pressed optic is alens.
 22. The solar energy system of claim 19, wherein said nubs assistin alignment of said pressed optic with said panel.